Device for adjusting the checking unit of a presser foot used in a sewing and/or embroidery machine

ABSTRACT

The invention relates to a device for adjusting a checking unit of a presser foot, used in a sewing or embroidery machine. A needle bar moves the presser foot towards a needle plate, using a spring which is connected in series. The checking unit intercepts the presser foot using a checking element of the unit, before contact is made with the work piece to be sewn and controls the movement of the presser foot until the latter touches the work piece. The checking element and the needle bar are both operated by a common drive and the bedding position of the checking element can be modified in relation to the needle plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a device for adjusting the checking unit of apresser foot of a sewing and/or embroidery machine.

2. Background Art

Throughout the following specification and claims, the terms “checking”and “check” and “catching” and “catch” may be used interchangeably.

An embroidery machine of this type with a checking unit for a presserfoot is known from DE 3117140. The checking unit disclosed in DE 3117140achieves a situation in which the presser foot no longer strikes theworkpiece to be machined and therefore the needle plate with the fullforce derived from the needle bar drive and transferred via the springinserted in between, but is checked shortly before contact, a large partof the force residing in the movement of the presser foot being absorbedbefore the presser foot is released to perform the remaining movementwith a certain time delay. The checking unit achieves a significantattenuation of the noise and protects the workpiece and/or theembroidery from damage caused by long term stress from the presser foot.The checking unit consists substantially of a control cam, whichactivates an angled lever, the one arm of which checks the presser foot,accelerated by a spring in the direction of the workpiece, via achecking component and releases the said foot with a time delay so thatthe presser foot is braked when it strikes the workpiece.

SUMMARY OF THE INVENTION

It is disadvantageous in the case of the checking unit known from DE3117140 that, resulting from the rigid structure, the movement path ofthe presser foot is identical for different thicknesses of workpiece sothat in the presence of relatively large workpiece thicknesses, thepresser foot strikes the surface of the workpiece with too much force sothat the advantages of the checking unit are reduced.

A device is described in DE 19628524, with which the presser foot ismoved into a safe position after the sewing process. No adjustment tomaterial thicknesses is provided.

A very time-consuming and expensive way is described in DE 4302094 inwhich the presser foot is moved via a separate drive motor thuspermitting any desired movement paths and therefore adjustment todifferent thicknesses of material to be implemented. However, theadditional drive requires a time-consuming synchronisation of the twodrives for the needle bar and the presser foot.

DE 4324741 and DE 2938894 show checking units for presser footattachments in which the movement path of the presser foot can beadjusted to the thickness of the material. It is disadvantageous inthese units that they utilise complicated lever systems which have anexpensive structure and are prone to breakdowns. Increased demands areimposed on the tolerances to be met because of the large number ofmoving parts and a relatively large amount of noise is created.

The object of the present invention is therefore to provide a checkingunit for a presser foot of a sewing machine which is of a simplestructure and permits an adjustment to a very wide range of workpiecethicknesses.

This object is achieved according to the invention by a device with thecharacteristics of claim 1.

It is advantageous in the device according to the invention that theposition of the bearing of the checking element, which works in directcombination with the presser foot, is changed manually or automaticallyand held and/or locked in a specific position. As a result, noadditional elements are necessary which have to be arranged in the forcetransmission region between the checking element and the drive for thechecking element. The adjustment of the position of the bearing of thechecking element, which is preferably an angled lever, should be able tobe moved to at least two positions or any desired location between twopositions and/or should be able to be locked.

In a particular embodiment of the device, the bearing and/or theswivelling axle of the checking element can be swivelled around an axis,so that the position of the checking element alters relative to theneedle plate depending on the angle set. To do this, the bearing of thechecking element itself is mounted in a cylinder coaxial to the latter'saxis, whereby the cylinder is mounted so that it can rotate around itsaxis on the sewing or embroidery machine.

If the cylinder is turned, the bearing which, for example may be a bolt,which is mounted so that it rotates in the cylinder coaxial to its axis,is moved around the axis, whereby the position of the bearing and/or thebearing bolt changes in respect of the needle plate. This permits anadvantageous thickness adjustment of the presser foot to the workpieceor embroidery by simple means. The cylinder itself is can be locked inany desired angle positions or at specific engaging points by means offixing screws or locking teeth which for example can be raised against aspring force.

The angle adjustment of the cylinder, mounted so that it can rotate,which holds the bearing for the checking element, can be performedautomatically by means of a drive in a further advantageous embodimentof the invention.

In a further embodiment, the bearing for the checking element is notmounted so that it can swivel around an axis but is able to be locked invarious positions especially parallel to the needle bar e.g. in alongitudinal slot. Moving the bearing in the longitudinal slot may beundertaken manually or automatically by means of a drive as in theembodiments described above.

In a further form of the embodiments described above, the materialthickness close to the presser foot is determined underneath the presserfoot by means of a sensor and the position of the checking element isregulated to correspond automatically by means of a drive. This has theadvantage of guaranteeing that even in the case of a workpiece which hasdifferent degrees of thickness at different points, the presser footalways strikes the workpiece in the bast possible way during theembroidery or sewing process.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are described in greater detailbelow on the basis of drawings.

These show:

FIG. 1 a side view of an embroidery head with a checking unit accordingto the invention;

FIGS. 2a+2 b: different settings for the position of the checkingelement;

FIG. 3 an exploded representation of the parts of an embroidery headrelevant to the checking unit;

FIG. 4 an exploded representation of a checking unit according to theinvention with an electric drive to adjust the bearing of the checkingelement automatically;

FIGS. 5a+5 b: Checking unit with distance sensor

FIG. 6: A multi-head embroidery machine with a central drive for thedevice according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a side view of the principal parts of the checking unit.The embroidery head 4, on which the parts of the checking unit and theneedle bar guide and the needle bar drive are arranged, is shown as adashed line. At least one cam disc 5, which deflects a cam lever 12,which is mounted so that it can swivel by means of the cam lever bearing2, is arranged on a shaft 4 a, which passes through and engages with theone embroidery head 4, or also further embroidery heads, if the shaft 4a is rotated. An angled lever 10, which forms the checking element andis mounted rotatably so that it can swivel around the axle 10 a isdeflected via a connecting rod 11. The free end of the one angle arm ofthe angled lever 10 supports a roller 9 which checks and releases thepresser foot 16, accelerated downwards by the spring F, according to themovement of the angled lever 10, which is specified by the design of theguide curve of the cam disc 5. The needle bar 17 is held by a guide 20and is driven via the needle bar drive 15, which is not shown in greaterdetail in FIG. 1. Like the angled lever 10, the needle bar drive 15 canbe driven by the shaft 4 a.

As is shown by FIGS. 2a and 2 b, by turning an eccentric bolt 7, theposition of the axle 10 a of the angled lever 10 can be adjustedrelative to the needle plate 19 and the embroidery material or workpiece18. The eccentric bolt 7 is mounted in a bearing bush 8 for this and canbe locked in any desired angle positions by means of a fixing screw 6(FIG. 3).

In addition to the adjustment of the height of the angled lever 10, itis possible to lock the swivelling axle of the cam lever 12 in differentpositions. The device has a bearing pin 2 a for this purpose, which isarranged eccentrically to an axis of rotation of the component 2. Thecomponent 2 rests in a bore with its cylindrical component 2 b in a bore3 a of a base plate 3 and is mounted in this so that it can rotate. Thebearing pin 2 a engages with the bore 3 a and serves as a bearing forthe cam lever 12. The component 2 can be locked in any desired anglepositions (arrows) in respect of the base plate 3 by means of a plate 1and a fixing screw 1 a. By rotating the component 2, the bearing pin 2 ais swivelled around the axis of rotation of the component 2 andtherefore changes its position.

A roller 14 or a ball bearing, which rests in the guide curve of the camdisc 5 and follows the latter when the cam disc 5 is rotated, is mountedon the one arm of the cam lever 12 on a pin 13. The other arm andtherefore the angled lever 12 is swivelled correspondingly.

FIG. 4 shows a further embodiment of the device according to theinvention, the structure of the device being substantially similar tothe embodiment according to FIG. 3, whereby, however, the eccentric bolt7 is replaced by an eccentric bolt 21 which has teeth (toothed wheel) onits one end which are connected to a servo-motor 22 via a toothed belt23. The eccentric bolt 21, and with it the bearing 10 a of the angledlever 10, are automatically adjusted by means of the servo-motor 22 andheld in position.

FIGS. 5a and 5 b show a further embodiment of the device according toFIG. 4, which possesses an additional sensor 24, which measures thethickness of the material and/or the distance of the surface of thematerial 18 from the sensor 24. The eccentric bolt 21 is turnedcorresponding to the sensor data, by means of the actuating drive 22,not shown, the swivelling axle 10 a of the angled lever 10 beingswivelled relative to the needle plate 19. The connecting rod 11 servesto compensate for the relative movements between the angled lever 10 andthe cam lever 12 during the adjustment either of the cam lever 12 or theangled lever 10 by means of the respective adjusting device.

In embodiments, which are not shown, the bearing and/or the swivellingaxle of the angled lever is not mounted so that it can swivel around anaxis but is moved in a linear manner, manually or by means of a drive,and locked in the position required. It is also feasible that thebearing and/or the swivelling axle can be moved along any desired pathsand locked.

FIG. 6 shows a multi-headed embroidery machine with a central drive 24,which drives eccentric bolts 21 of the individual embroidery heads 4 ofthe machine via a shaft 27 and toothed belts 23, whereby it is possibleto make a simultaneous height adjustment of the presser foot attachmentsof all the embroidery heads simultaneously. As all the embroidery headsusually embroider identical embroidery designs, it is sufficient todetermine the distance between the surface of the embroidery and theneedle plate on just one embroidery head or embroidery design in orderto undertake the height adjustments for all the embroidery headssimultaneously on the basis of the distance determined. In anembodiment, which is not shown, couplings are provided between the shaft27 and the eccentric bolt 21 so that the height adjustment of specificembroidery heads 4 can be switched on or off optionally, depending onthe requirement. Thus in multi-headed embroidery machines, e.g. as aconsequence of the size of the embroidery design, often only certainembroidery heads are required such as e.g. every second, third etc.embroidery head. The other embroidery heads are disconnected from themain drive shaft. In this case the couplings can be used to switch offthe presser foot attachments of the embroidery heads which are notrequired.

What is claimed is:
 1. Device for adjusting a catching unit of a presserfoot (16) of a sewing or embroidery machine, a needle bar (17) movingthe presser foot (16) in the direction of a needle plate (19) includingthe action of a spring (F) and the catching unit catching the presserfoot (16) before it strikes the workpiece (18) to be processed by meansof a catching element (10) of the catching unit and controlling itsmovement up to striking the workpiece (18), the catching element (10)being driven by a common drive together with the needle bar (17)characterised in that the bearing forming the axle (10 a) of thecatching element (10) is arranged axis-parallel to the axis of rotationof a rotating body (7), the rotating body (7) being mounted on thesewing machine so that it rotates, the position of the bearing beingadjustable relative to the needle plate (19) by turning the rotatingbody (7).
 2. Device according to claim 1, characterised in that therotating body (7) can be locked in a specific position by means of alocking element (6).
 3. Device according to claim 2, characterised inthat the rotating body (7) can be turned by means of a drive (22) andcan be held and/or locked in at least one position.
 4. Device accordingto claim 2, characterised in that the locking element is a fixing screw.5. Device according to claim 1 characterized in that the catchingelement (10) is an angled lever.
 6. Device according to claim 1characterized in that the bearing and/or the axle (10 a) can be lockedin at least two positions relative to the needle plate (19).
 7. Deviceaccording to claim 1 characterized in that the movement of the catchingelement (10) is controlled by a control cam (5) driven dependent on theneedle bar drive.
 8. Device according to claim 7, characterised in thata compensation element is inserted between a cam lever (12) moved by thecontrol cam and the catching element (10).
 9. Device according to claim8, characterised in that the compensating element is a connecting rod.10. Device according to claim 8, characterised in that the cam lever(12) is an angled lever, which is mounted around an axle (2 a) on thesewing machine so that it can swivel, the position of the axle (2 a)being adjustable relative to the axle (4 a) of the control cam (5) bymeans of an adjusting device (2) and able to be locked in variouspositions by means of a locking device (1).
 11. Device according toclaim 10, characterised in that the locking device is a fixing screw.12. Device according to claim 1 characterized in that a controldetermines the thickness of the workpiece close to at least one presserfoot (16) by means of at least one sensor (24) and, using the drive(22), sets or regulates the position required for the catching element(10) for the workpiece thickness established.
 13. Device according toclaim 12 characterized in that the control adjusts or regulates theposition required for the catching element (10) continuously or atpredefined intervals during the sewing process.
 14. Device according toclaim 1 characterized in that the height adjustment of the presser footattachments (16) of the embroidery heads (4) is undertaken by a commondrive (24).
 15. Device according to claim 14, characterised in that acommon shaft (27) connects the drive (24) to the means of adjustment tomove or advance the bearing or the axle (10 a).
 16. Device according toclaim 15 characterised in that at least one coupling is arranged betweenthe shaft (27) and each bearing and/or each axle (10 a).
 17. Device foradjusting a catching unit of a presser foot (16) of a sewing orembroidery machine, a needle bar (17) moving the presser foot (16) inthe direction of a needle plate (19) including the action of a spring(F) and the catching unit catching the presser foot (16) before itstrikes the workplace (18) to be processed by means of a catchingelement (10) of the catching unit and controlling its movement up tostriking the workpiece (18), the catching element (10) being driven by acommon drive together with the needle bar (17), the position of thebearing of the catching element (10) being alterable relative to theneedle plate (19) characterised in that a control determines thethickness of the workpiece close to at least one presser foot (16) bymeans of at least one sensor (24) and, using the drive (22), sets orregulates the position required for the catching element (10) for theworkpiece thickness established.